1. Field of the Invention
The present invention relates to a constant velocity universal joint, in particular, to a sliding type tripod constant velocity universal joint.
2. Description of the Related Art
Generally, a constant velocity universal joint is a kind of universal joint, which couples a driving shaft and a driven shaft with each other and allows the transmission of torque at a constant velocity even if an angle is formed between the two shafts (not aligned straight). Among the constant velocity universal joints, a sliding type enables relative axial displacement between two shafts by plunging a joint. As one kind of the sliding type constant velocity universal joint, a tripod type constant velocity universal joint is widely known. The tripod constant velocity universal joint is configured so that a tripod member having three trunnions protruding in a radial direction is connected to one of the shafts whereas a hollow cylindrical outer joint member having three track grooves extending in an axial direction is connected to the other shaft. The trunnions of the tripod member are housed within the respective track grooves of the outer joint member so as to transmit a torque.
In the existing tripod type constant velocity universal joint, a roller is rotatably fitted onto a cylindrical outer circumferential face of each of the three trunnions of the tripod member, which protrudes in the radial direction of the tripod member, through a plurality of needle bearings. The roller rolls on roller guiding faces of the track groove. The position of the roller with respect to the trunnion is fixed (in a coaxial state). Therefore, when torque is transmitted while the joint forms a working angle, the roller and the roller guiding faces diagonally cross each other. As a result, a slide occurs between the roller guiding faces and the roller to generate a slide resistance, which in turn generates an induced thrust in the axial direction. Such a slide resistance and an induced thrust cause the vibration and noise of a vehicle body, affecting noise, vibration, harshness (NVH) performance of the vehicle to decrease the freedom of design of the underbody of a vehicle. Therefore, it is desirable to lower the slide resistance and the induced thrust as much as possible.
A tripod type constant velocity universal joint disclosed in Japanese Patent Laid-Open Publication No. 2000-320563 has been proposed as a sliding type tripod constant velocity universal joint which intends to lower such slide resistance and induced thrust. The disclosed joint includes: rollers inserted into track grooves of an outer joint member; and rings fitted onto trunnions of a tripod member so as to rotatably support the rollers. An inner circumferential face of each of the rings is formed to have a circular-convex cross section. At the same time, an outer circumferential face of the trunnion is formed to have a straight shape on a longitudinal section and, on its cross section, is in contact with the inner circumferential face of the ring in a direction perpendicularly crossing an axial line of the joint with gaps formed between the inner circumferential face of the ring and the outer circumferential face of the trunnions in the axial direction of the joint.
In the invention of the above-cited patent publication, a roller assembly including the ring and the roller is capable of oscillating with respect to the trunnion. Therefore, when the joint forms a working angle, the trunnion can be inclined with respect to the outer joint member without changing the position of the roller assembly. Accordingly, since the position of the roller assembly becomes constantly stable so that the roller is kept parallel to the roller guiding faces, the roller can smoothly roll. Such a structure can contribute to reduction of the slide resistance, and in turn, to reduction of the induced thrust.
In the constant velocity universal joint described in the above-mentioned patent publication, as shown in FIG. 5, an outer circumferential face of a roller 34 is formed in a convex-curved shape having an arc with a center of curvature on a center axis of a trunnion 22 or at the position separate from the center axis of the trunnion 22 in a radial direction as a generatrix in view of the functions.
Outer joint members, which can be used as an outer joint member 10 in the tripod type constant velocity universal joint described in the above-mentioned patent publication, can be roughly classified into two types as shown in FIGS. 6(A) and 6(B); an outer joint member having flanges 17 in a track groove 12 on the outer diameter side of roller guiding faces 14 (FIG. 6(A)), and an outer joint member having a cylindrical large inner diameter portion 15, omitting the flanges (FIG. 6(B)). In the no-flange type (FIG. 6(B)), in particular, when the joint turns with no load such as in the case where a vehicle runs only by an inertia force, a roller 34 shifts from its normal position (in a state where the roller is kept parallel to the roller guiding faces) to be likely to be inclined because of the relation with the outer circumferential shape of the roller, as shown in FIG. 5 (the inclination herein means that the center axis of the roller is inclined on a plane containing the center axis of the joint; this meaning is also applied to the following description).
In the case where such inclination occurs, a part of the roller assembly, for example, an end face 34b of the roller 34 on the outer diameter side may sometimes be in contact with the large inner diameter portion 15 between the roller guiding faces 14. If the joint turns in such a state, sliding friction occurs at an interfered portion, which may sometimes increase the amount of abrasion of the large inner diameter portion 15.